Anyone have a parts drawing of an SME Series III?

I am putting together a Thorens 160 tt with an SME Series III tonearm. I had to pull the SME tonearm off another armboard and either lost a part, or just forgot how the bearing / and grounding parts were assembled. Specifically, there is a white plastic cylinder that slides onto the main bearing (upwards). It has a ground connection, and contact point (appears to be magnetic) to ground the tonearm. What holds it in place? A spring?